1. Field of the Invention
The present invention relates to a method for producing a liquid transport apparatus which transports a liquid by applying a pressure to the liquid contained in a pressure chamber, and a method for producing a piezoelectric actuator to be used for such a liquid transport apparatus.
2. Description of the Related Art
A common electrode is arranged in a substantially entire region of a lower surface of a piezoelectric layer which covers pressure chambers in an ink-jet head described in Japanese Patent No. 3396196, Individual electrodes are arranged on an upper surface of the piezoelectric layer so that they are opposed to substantially central portions of the pressure chambers. Further, auxiliary individual electrodes are arranged so that they are opposed to portions of the pressure chambers, the portions being disposed on the outer side as compared with portions of the pressure chambers opposed to the individual electrodes. When the voltage is applied between the individual electrode and the common electrode to shrink a portion of the piezoelectric layer by generating the electric field at the portion of the piezoelectric layer interposed between the electrodes, a constraint plate, which is arranged on the upper surface of the portion of the piezoelectric layer opposed to the individual electrode, is deformed. Further, simultaneously therewith, when the voltage is also applied between the auxiliary individual electrode and the common electrode to elongate the portion of the piezoelectric layer interposed between the electrodes by generating the electric field in the direction opposite to the above at the portion of the piezoelectric layer interposed between the electrodes, then the portion of the piezoelectric layer, which is interposed between the individual electrode and the common electrode, is shrunk easily, and the amount of deformation of the constraint plate is increased.
An ink-jet head type recording head described in Japanese Patent Application Laid-open No. 2000-6396 includes a lower electrode film, a piezoelectric layer, and an upper electrode film which are arranged and mutually stacked in this order from the bottom, on an upper surface of an elastic film which covers pressure chambers. The piezoelectric layer and the upper electrode film are divided into portions which are opposed to substantially central portions of the pressure chambers and portions which are opposed to ends of the pressure chambers and portions disposed between the adjoining pressure chambers respectively. The portions of the piezoelectric layer, the upper electrode film, and the lower electrode film, which are opposed to the substantially central portions of the pressure chambers, serve as first piezoelectric vibrators, and the portions of the piezoelectric layer, the upper electrode film, and the lower electrode film, which are opposed to the ends of the pressure chambers, serve as second piezoelectric vibrators. In this arrangement, the portion of the elastic film, which is opposed to the pressure chamber, is pulled upwardly by applying the voltage to the second piezoelectric vibrator to shrink the portion of the piezoelectric layer for constructing the second piezoelectric vibrator. After that, the second piezoelectric vibrator is released from the application of the voltage, and the voltage is applied to the first piezoelectric vibrator to shrink the portion of the piezoelectric layer for constructing the first piezoelectric vibrator. Accordingly, the portion of the elastic film, which is opposed to the pressure chamber, is deformed so that the portion projects toward the pressure chamber, and thus the ink is discharged from the nozzle. When the elastic film is once pulled upwardly, and the deformation is thereafter brought about to project toward the pressure chamber as described above, then it is possible to increase the amount of deformation of the elastic film.
In the case of an ink-jet head described in Japanese Patent Application Laid-open No. 2004-136461, a plurality of electrodes are buried or embedded in a piezoelectric layer in the in-plane direction thereof. Mutually adjoining portions, which are included in a plurality of portions interposed between the plurality of electrodes of the piezoelectric layer, are polarized in the opposite directions.
In the case of an ink-jet head described in Japanese Patent Application Laid-open No. 2002-292865, first electrodes are arranged respectively at portions of a piezoelectric layer opposed to walls disposed on both sides of pressure chambers in relation to one predetermined direction, and second electrodes are arranged at portions of the piezoelectric layer opposed to substantially central portions of the pressure chambers. As for the piezoelectric layer, the portion which is disposed between the second electrode and the first electrode arranged at the portion opposed to one of the walls of the pressure chamber and the portion which is disposed between the second electrode and the first electrode arranged at the portion opposed to the other wall of the pressure chamber are polarized respectively in directions inclined toward the mutually opposite sides in relation to the in-plane direction of the piezoelectric layer with respect to the thickness direction of the piezoelectric layer from the second electrode toward the first electrode.
In view of the above, in relation to the descriptions of Japanese Patent No. 3396196 and Japanese Patent Application Laid-open Nos. 2000-6396, 2004-136461, and 2002-292865, the inventors of the present invention have found out that an advantageous situation arises in the design of the piezoelectric actuator when the two adjoining portions of the piezoelectric layer are polarized in the mutually opposite directions in the piezoelectric actuator in which the electrodes are arranged so that the mutually adjoining portions of the piezoelectric layer are interposed respectively as described in Japanese Patent No. 3396196 and Japanese Patent Application Laid-open No. 2000-6396.
However, when the two adjoining portions of the piezoelectric layer are polarized in the mutually opposite directions, if the electric field is generated in order to polarize one of the two portions, then the polarization of the other is weakened by the electric field. As a result, it is feared that the amount of deformation of the piezoelectric layer may be decreased.